Biomass boiler case study

An operational issue in achieving the correct temperatures in the poultry sheds was the first indication that there was a major problem within the system. The overhead heaters in the poultry sheds were inspected and found to be blocked with black deposits. The black deposits were restricting water flow and reducing heat transfer which was the reason why the correct temperatures could not be achieved in the poultry sheds.

The system water was sampled at various parts of the system and the analysis showed that the soluble and suspended iron levels in the system water were very high, particularly in the samples taken from the boiler.

Solution

The black deposits were the result of corrosion of both the boiler and the system pipe work because the system had operated for 18 months with no corrosion protection.

The solution to the problem was a three phase approach:

1. Clean the system to remove the blockages and restore heat transfer
2. Apply a passivation treatment to arrest the corrosion of the system
3. Dose a corrosion inhibitor to maintain corrosion at acceptable low levels

Phase 1 – Clean

Each individual overhead heater was physical cleaned to remove the majority of the

black deposit and then they were flushed individually using a small flushing rig. The heaters were flushed using DHS 3800 dosed at 1% in the recirculating water.

When all the overhead heaters had been individually flushed the whole system was cleaned using a 1% solution of DHS 3800. 

After the cleaning of the system selected overhead heaters were inspected to make sure they were still clean and had not trapped any of the debris liberated during the full system cleaning process. 

Phase 2 – Passivation

The system was treated with DHS Passivator dosed at 0.5% (0.5 litres per 100 litres of system water). DHS Passivator is a corrosion inhibitor designed to quickly promote the formation of a protective film.

Phase 3 – Corrosion Inhibition

The system was treated with DHS 3050 dosed at 0.5% (0.5 litres per 100 litres of system water). DHS 3050 has been formulated as a multipurpose treatment to inhibit metal corrosion and scale in all types of waters. The concentration of inhibitor in the system was monitored to establish that the correct dose was being applied.

Result

Cleaning the system re-established the correct water flow rates and restored the heat transfer. This resolved the problem of control over the temperatures and the correct temperatures could be achieved in the poultry sheds.

The passivation treatment and use of an effective corrosion inhibitor provided control over the corrosion of the system.

Analytical Parameter	Units	Before  Treatment	After  Treatment
Total Iron	mg/l	125.0	4.5
Soluble iron	mg/l	14.5	2.3
Soluble Copper	mg/l	1.2	0.2

 

The total iron and soluble iron and soluble copper levels have dramatically decreased after using the DHS Passivator and DHS 3050 compared to what the levels were with no treatment.

Instantaneous corrosion rates for mild steel measured with a corrater probe also showed a dramatic reduction in corrosion rates from 0.218 mm/y with no treatment down to 0.012 mm/y with treatment.

Conclusion

BioMass boilers are becoming popular, particularly within the farming community because of their environmentally friendly aspects and the availability of relatively inexpensive fuel. The systems can be filled with a variety of water qualities and many use town’s mains water. In some cases the boiler manufacturer recommend the use of softened or demineralised water to fill the system. The quality of water used can vary from softened or naturally soft water through to hard water depending on the location or the instructions of the manufacturer. In many cases the need to treat the boiler water to prevent the problems of scale and corrosion is either overlooked or thought not to be necessary.

This case study highlights the problems that can occur by operating a hot water boiler like a BioMass boiler without using any treatment. After 18 months of operating with no treatment the overhead heaters used to control the temperatures in the poultry sheds were almost completely blocked with corrosion debris (black iron oxide) which severely restricted water flow and reduced heat transfer. The black iron oxide was generated from corrosion of the boiler and the system pipework. The majority of the corrosion has taken place in the boiler itself and if this was allowed to continue it would seriously reduce the life expectancy of the boiler.

To effectively treat a hot water boiler like a BioMass boiler it needs to be treated with an effective multipurpose corrosion inhibitor like DHS 3050 from the first time the boiler is filled with water. When the BioMass boiler is operational water samples should be taken on a quarterly basis and analysis carried out. The level of inhibitor needs to checked and the inhibitor should be topped up if below the recommended level. The iron and copper levels should be measured to monitor that corrosion is under control.

Alternatively, if the use of a treatment has been overlooked or the control of the treatment has been neglected this case study demonstrates that it is possible to recover the situation.

The use of the three phase approach:

1. Clean the system to remove the blockages and restore heat transfer using an effective cleaner such as DHS 3800. This can also be combined with a side-stream filter to remove suspended matter, reduce flushing times and reduce the amount of water required during flushing.
2. Apply a passivation treatment such as DHS Passivator to rapidly generate a protect film and reduce the corrosion of the system
3. Dose a multi-purpose corrosion inhibitor such as DHS 3050 to maintain corrosion at acceptable low levels.

 

BioMass boilers are an expensive piece of equipment and the water systems must be treated to prevent scale and corrosion, and the systems need to be monitored quarterly for treatment levels and performance to ensure trouble free operation and to achieve the expected lifetime of the boiler.